The present invention relates to a method for etching electrode foil for aluminum electrolytic capacitors.
The so-called aluminum electrolytic capacitor is constituted by rolling an aluminum electrode foil and an insulating paper and impregnating the roll with an electrolyte for its driving. In this capacitor, the aluminum electrode foil has its surface undulated to increase its area by etching it, thereby increasing the elevating surface enlarging factor (surface area after etching/surface area before etching) of the aluminum foil is used. Heretofore, as the methods for etching the electrode foil for the aluminum electrolytic capacitors mainly for use at such a low voltage as less than 100 W.V., the following two methods normally have been normally employed.
Thus a first method is that using an etching solution of hydrochloric acid as its main component. The etching is performed, with placing an aluminum foil between two electrode plates facing each other and in parallelism thereto and with allowing an alternating current flowing to through the etching solution between the two electrode plates, without current directly flow through the aluminum foil.
A second method is that using an etching solution of sodium chloride as its main component. The etching is peformed, with immersing an aluminum foil in this etching solution, and by permitting a direct current or alternating current or alternating current-superposed direct current to flow in the etching solution between the aluminum foil and an electrode or electrodes placed on one or both sides of the aluminum foil.
However the first etching method was disadvantageous in that only a current that has symmetrical wave forms in its positive and negative cycle permits independent changes in its positive and negative wave width and in its positive and negative current densities, thus detracting from adequate enhancement of the surface enlarging factor, all the more so in view of the searching for on further miniaturization hereafter of aluminum electrolytic capacitors. The second etching method had a grave defect in that because of the use of a nearly neutral aqueous solution of sodium chloride as the etching solution, the aluminum ion which dissolves during electrolytic etching deposits on the production equipment or the like as hydroxide thereof (white powder); which interferes with smooth proceeding of production and upgrading of operation rate.